1. Field of the Invention
This invention pertains to spinal implants and surgical procedures for use in spinal stabilization. More particularly, this invention pertains to an apparatus and method for implanting a tapered implant between two vertebrae.
2. Description of the Prior Art
Chronic back problems can cause pain and disability for a large segment of the population. In many cases, the chronic back problems are attributed to relative movement between vertebrae in the spine.
Orthopedic surgery includes procedures to stabilize vertebrae. Common stabilization techniques include fusing the vertebrae together. Fusion techniques include removing disk material which separates the vertebrae and impacting bone into the disk area. The impacted bone fuses with the bone material in the vertebrae to thereby fuse the two vertebrae together.
To increase the probability of a successful fusion, spinal implants have been developed. Commonly assigned U.S. Pat. No. 5,489,307 discloses a hollow threaded cylindrical implant. That patent also discloses a method of placing the implant between two vertebrae.
The method of U.S. Pat. No. 5,489,307 discloses parallel distraction of opposing vertebrae prior to placing an implant. However, not all vertebrae are in parallel opposition. A normal and healthy spine has a natural curvature referred to as lordosis. As a result of the curvature, opposing vertebrae are positioned with their end plates in non-parallel alignment depending upon the position in the spine. For example, in the lumbar region of the spine, the end plates of the L-4 and L-5 vertebrae may be at an angle of about 3.degree.-15.degree.. Similarly, the opposing end plates of the L-5 and S-1 vertebrae may be at about 8.degree.-16.degree. lordosis. The actual amount of lordosis varies with the location of the spine and varies from patient to patient. It is desirable to provide an implant which maintains or achieves a desired lordosis between opposing vertebrae and a method of placing the implant.